Maybe both? Working for the IT dept of a mid sized company I usually get hit will all the cell phone or cheap smartphone questions. Even a few cheap PDA questions though those have fallen off in the last year.

Cheap smart phones are getting a lot easier to come by now that they have been out for more than 5 years. Now the through ebay you can get the cheapest smart phones that are only partially used or even new. Though I would stick with the used ones for the big discounts. Thinking that you need email and text services you can pick up Samsung smartphones like the blackjack II with older windows mobile and hook it right to your exchange server and if you get the right plan with data and texting you are good to go.

If you are using cdma services though like verizon you can be a little more limited to some of the motorola que series or blackberry. I would stay away from blackberry as it takes more support effort to make sure email and attachments and anything really to work.

The best smartphone for you? Well that would be the phone with the right mix of features and be a cheap pda as well with calendaring and contact management. Unless you get an iphone I would go with a phone with a full keyboard as the digital keyboard on the windows based phones are terrible. The google based android smartphones are getting closer to iphone status but not there quite yet.
 
The cheapest mobile phones are still the used ones on ebay. If you can find a phone that is just over a year past it's introduction date then you can see how the cost curve swings in the purchaser's favor after that point. Yes I have been watching phone prices for a long time.

For some really good deals right now on locked and unlocked smartphones look at the Samsung omnia, and blackjack II. The Motorola Que with windows mobile 6 (not the palm based smart phone) and the HTC Tytn II or otherwise known as the TILT.

Easiest of use and setup goes to the Blackjack II. It does not have a touchscreen so web browsing is sub par but for connecting to an exchange server and syncing with your mailbox and calendar it gets the job done and is super cheap.

Top of the heap best smartphone is the iphone. It flat out does it all and does it well. With version 2 and higher firmware you can now sync with exchange. You just have to have AT&T which are terrible. but you can get a refurb v2 version for $99 which is a steal.